Microsoft today unveiled a public sneak peek of its newest browser, Internet Explorer 9 (IE9), aimed at Web developers and the technically brave of heart.

"The Platform Preview, and the feedback loop it is part of, marks a major change from previous IE releases," said Dean Hachamovich, the browser team's general manager, in a statement issued today before he took the stage at MIX10, Microsoft's Web developer conference, to publicly launch IE9.

Hachamovich promised that Microsoft would update the IE9 preview about every eight weeks, putting the first such update in mid-May with another to follow in mid-July. He did not, however, disclose a release schedule for the successor to 2009's IE8, the browser bundled with Windows 7.

IE 9 Platform Preview is far from polished, or even finished, Microsoft acknowledged, which is why it has slapped the moniker on the release, a first for IE.

"While it loads and renders Web pages using the Internet Explorer 9 platform, it is not designed to be a complete Web browser," Microsoft said in a fact sheet that accompanied the preview's announcement. "This build is simply a first look at the work Microsoft has done so far and is ready to share with its developer community."

To give Web site designers, application developers, and others who want to track the new browser's progress a chance to try IE9, Microsoft has created what it called a "Test Drive" site that showcases the features and enhancements included in the preview.

The Platform Preview will run only in Windows 7, Windows Vista Service Pack 2 (SP2) and Windows Server R2. The latter two operating systems require the Platform Update that Microsoft shipped last October. That update was notable for adding other Windows 7 features, such as that operating system's ribbon-style interface, to Vista last year.

The preview will not run on Windows XP, the operating system that accounts for more than 71% of all Microsoft-made operating systems in use worldwide.

"Internet Explorer 9 requires the modern graphics and security underpinnings that have come since 2001, and is intended to be run on a modern operating system in order to build on the latest hardware and operating system innovations," a company spokeswoman said in an e-mail reply to Computerworld's questions Tuesday morning.

IE9, which Microsoft again touted for its performance gains, taps the PC's graphic processor to boost text and graphics rendering speeds using the Direct2D and DirectWrite APIs (application programming interfaces). Support for those APIs is built into Windows 7, and added to Vista and Server 2008 R2 with the October 2009 Platform Update.

Unlike full-fledged editions of IE, the IE9 Platform Preview does not replace existing versions of IE -- such as IE7 on Vista or IE8 on Windows 7 -- but runs alongside them on the same PC.

The preview is a 31MB download, and can be retrieved from the Test Drive site that Microsoft has set up.

IE9 Platform Preview isn't a full-fledged browser, but just the bare rendering bones.